I shot the following picture with a Canon AE-1 Program on a roll of Ilford HP5 400 (I pushed the roll to 800). I developed it using Ilfosol 3 and scanned it with Epson scanner V370. As you can see, there are - I'm not sure how to describe them - smudge like shadows corresponding to the perforations. The shadows are only on the third frame of the roll. I am left to wonder what caused these on only one frame, and what can I do in the future to prevent it from happening?
The effect is even easier to see on the negative: